w126 300sel smoke odor

[xaliscomex]

Own a 1988 300sel w126 and have been noticing for some time a smoke/burnt oil smell when driving. Rolling down the windows seems to dissipate the odor. I'm not sure where the smell is coming from. I don't think its the exhaust. Seems like there is a drop of oil maybe making contact with the exhaust. I close the vents which prevent the outside, i think, air from coming in. What would be giving off such an unpleasant oil or exhaust smell. Hard to really say what exactly it is..Please advise